<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box-1:hover{
            background-color: aquamarine;
            width: 300px;
        }

        ul li:nth-child(1){
            background-color: yellow;
        }
        /* 根据奇数/偶数选择对应标签 */
        ul li:nth-child(even){
            background-color: red;
        }
    </style>
</head>
<body>
    <div class="box-1">div标签</div>
    <ul>
        <li>css定位</li>
        <li>css元素堆叠</li>
        <li>css浮动</li>
        <li>python</li>
        <li>java</li>
        <li>golang</li>
    </ul>
</body>
</html>